DE 103 23 567 A1 discloses a method and device for controlling the slip of a friction clutch. In this context, a clutch actuator is controlled by a control device in such a way that a predefined slip between the friction clutch, which is mounted on the crank shaft of an internal combustion engine and a clutch disk, which bears friction linings and is connected to the gear mechanism input shaft of a gear mechanism is set on the friction clutch, in order to reduce or eliminate grabbing during the coupling-in phase of the friction clutch. In this context, the clutch actuator is modulated by the control device with respect to its advancing movement. The clutch actuator contains an electronically commutated electric motor, which commutates on the basis of Hall sensors, arranged over the rotational axis of the rotor, and the signals thereof, and is controlled with respect to its rotational speed. Such an electronically commutated electric motor is known, for example, from DE 10 2006 017 146 A1. In this context, the rotation of the rotor is determined incrementally by means of a plurality of Hall sensors distributed over the circumference, by determining the switching points of the Hall sensors when there is a change of polarization of magnets rotating past the Hall sensors. Angular increments, which supply a predefined angular resolution as a function of a predefined number of Hall sensors, are determined therefrom. In order to be able to determine a smoothed rotational speed profile of the rotor, it is possible to average between two or more discretely determined incremental angular values.
The data which is acquired from the signals and evaluated is used to control the commutation of the electric motor. In this context, a power transistor is switched in a digital manner under conditions which apply to the commutation of a magnetizable magnet segment such as the winding, and when the conditions apply to the next winding is switched off again. Accordingly, the rotor is then driven in digitized fashion as a manner of the resolution of the Hall sensors. The driving is unnoticeable at relatively high rotational speeds. When slip regulation of a friction clutch is applied, the friction clutch is moved comparatively quickly over predefined axial travel by the clutch actuator, During travel the slip is regulated with a predefined slip rotational speed. The axial travel of the friction clutch and therefore, the clutch actuator for regulating the slip rotational speed is very low here, with the result that correspondingly small rotational angles of the rotor are necessary. The rotational angles can be in angular ranges of the angular resolution of the Hall sensors, for example between two switching points of two Hall sensors which are adjacent in the circumferential direction. In this way, slip control is possible only with a comparatively large control width and therefore increased slip rotational speeds, which leads to increased wear-inducing feeding of heat into the friction clutch and therefore to a higher consumption of fuel.